Extent of oxidation of Cr(III) to Cr(VI) under various conditions pertaining to natural environment

Apte, Amita D; Tare, Vinod; Bose, Purnendu

doi:10.1016/j.jhazmat.2005.07.057

Cited by 189 publications

(71 citation statements)

References 20 publications

(38 reference statements)

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“…Mining, smelting, industrial activities and traffic activities are primary sources of heavy metal pollution [1][2][3]. Series of physical, chemical and biological reactions, such as sorption-desorption [4], ion exchanges, complexation [5], oxidation-reduction [6], precipitation [7], and bioaccumulation [8], will occur, once heavy metal enters water bodies. The sorption of heavy metals onto suspended and riverbed sediments can reduce their concentration in aquatic systems, whereas desorption can lead to secondary heavy metal pollution [9,10].…”

Section: Introductionmentioning

confidence: 99%

Binary Component Sorption of Cadmium, and Copper Ions onto Yangtze River Sediments with Different Particle Sizes

2017

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Sorption is a crucial process that influences immobilization and migration of heavy metals in an aqueous environment. Sediments represent one of the ultimate sinks for heavy metals discharged into water body. Moreover, the particle size of sediments plays an extremely important role in the immobilization of heavy metals. In this study, the sorption and desorption of cadmium (Cd) and copper (Cu) onto sediments with different particle sizes were investigated to predict the rate and capacity of sorption, to understand their environmental behaviors in an aqueous environment. Batch sorption and kinetic experiments were conducted to obtain the retained amount and rate of Cd and Cu in a binary system. Experimental data were simulated using sorption models to ascertain the sorption capacity and the kinetic rate. Results of European Communities Bureau of Reference (BCR) sequential extraction showed the highest concentration of Cd (0.344 mg kg −1 ), and its distribution varied with sediment particle size and site. Furthermore, most of Cu (approximately 57% to 84%) existed as a residual fraction. The sorption of Cu onto six sediments followed a pseudo-first order reaction, whereas that of Cd followed a pseudo-second order reaction. Additionally, the competitive Langmuir model fitted the batch sorption experimental data extremely well. The highest sorption capacities of Cd and Cu reach 0.641 mmol kg −1 and 62.3 mmol kg −1 , respectively, on the smallest submerged sediment particles. The amounts of Cu and Cd desorbed (mmol kg −1 ) increased linearly with the initial concentration increasing. Thus, sediment texture is an important factor that influences the sorption of heavy metal onto sediments.

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Section: Introductionmentioning

confidence: 99%

Binary Component Sorption of Cadmium, and Copper Ions onto Yangtze River Sediments with Different Particle Sizes

2017

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“…This conclusion is supported by experiments in which no significant chromate species were found in the solution bubbled with only air for more than 300 h. 9 In contrast, the Cr 3+ /Cr 6+ reaction has been reported to occur in atmospheric oxygen at high temperature during a bush fire 10 and also with the presence of MnO 2 oxidant in the natural sea water. 11,12 In the case of TCC coatings, chromate formation has been attributed to the transient formation of hydrogen peroxide generated by oxygen reduction. The influence of H 2 O 2 has been explored by Li et al, 13 who immersed TCC coated AA2024 alloy in 0.5 M Na 2 SO 4 solutions with addition of 0.01, 0.1 and 1 v/v % H 2 O 2 for 1 h. A small level (0.01% v/v) of H 2 O 2 can significantly promote the formation of chromate species and Raman intensities associated with chromate species increased in proportion to the concentration of H 2 O 2 .…”

mentioning

confidence: 99%

Chromate Formed in a Trivalent Chromium Conversion Coating on Aluminum

Gao

Liu

et al. 2017

J. Electrochem. Soc.

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This present study employs aluminum substrates to investigate the formation of Cr(VI) species during a trivalent chromium conversion coating process. The study had a particular focus on understanding the influences of copper in the substrate and O 2 , ZrF 6 2− and F − in the bath on the formation of Cr(VI) species, which were detected by Raman spectroscopy. Comparison of electropolished aluminum and sputtering-deposited aluminum substrates revealed greatly increased rates of coating growth associated with an enrichment of copper impurity in the electropolished substrate that was revealed by transmission electron microscopy. With respect to chromium chemistry in a developed coating, the presence of dissolved oxygen and long conversion treatment times promoted the formation of Cr(VI) species that are generated by oxidation of Cr(III) species. The Cr(III) species are oxidized by H 2 O 2 , which was produced by oxygen reduction reaction. The generation of H 2 O 2 was demonstrated by analysis of the treatment bath using UV spectrophotometry. Conversion coating processes are employed as surface pretreatments of aluminum and aluminum alloys to improve the adhesion with organic primers and increase corrosion protection. Chromate conversion coating (CCC) has been widely used as a conventional and effective process in the aerospace and automotive industries.1-3 However, the toxicity of chromates to human beings and the detrimental impact of chromates on the environment are giving rise to greater regulation of their use. 4,5 In contrast, trivalent chromium species are relatively eco-friendly and, hence, trivalent chromium conversion (TCC) coating processes are being investigated as promising alternatives to CCC processes. 6The TCC coating bath generally contains hexafluorozirconate, sodium fluoride and trivalent chromium sulfate, which results in coatings formed on aluminum that contain Zr-/Cr-rich oxides, hydroxides and fluorides.6-8 Interestingly, a freshly-formed TCC coating after a conversion treatment for 1200 s in a naturally-aerated bath displayed chromate presence by a Raman shift at 866 cm −1 , but the peak intensity was negligible in a coating formed in a deoxygenated bath. 8 Notably, the oxidation of Cr 3+ to Cr 6+ in the aqueous electrolyte is not due solely to the presence of dissolved oxygen. This conclusion is supported by experiments in which no significant chromate species were found in the solution bubbled with only air for more than 300 h. 9 In contrast, the Cr 3+ /Cr 6+ reaction has been reported to occur in atmospheric oxygen at high temperature during a bush fire 10 and also with the presence of MnO 2 oxidant in the natural sea water. 11,12 In the case of TCC coatings, chromate formation has been attributed to the transient formation of hydrogen peroxide generated by oxygen reduction. The influence of H 2 O 2 has been explored by Li et al.,13 who immersed TCC coated AA2024 alloy in 0.5 M Na 2 SO 4 solutions with addition of 0.01, 0.1 and 1 v/v % H 2 O 2 for 1 h. A small level (0.01% v/v) of H 2 O 2 ca...

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“…Therefore, it is reasonable to presume that dissolved Mn could be indicative of Cr(III) oxidation. Though, there are reports on the MnO 2 oxidation of Cr(III) in natural waters (Fantoni et al 2002;Apte et al 2006), the occurrence of such oxidation reaction has not been supported by some studies (Armienta and Quere 1995;Gonzalez et al 2005). In some of the samples (5, 49, 53, 60), the concentration of dissolved Mn was more than 10-fold compared to that of Fe(II) and Cr(VI) concentrations.…”

Section: Temporal Variation Of Chromium Speciesmentioning

confidence: 89%

Chromium speciation in a contaminated groundwater: redox processes and temporal variability

Kumar

Riyazuddin

2010

Environ Monit Assess

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Chromium species (Cr(III), Cr(VI), and Cr(III)-organic) in groundwater of a tannery contaminated area were monitored during pre- and post-monsoon seasons for a period of 3 years (May 2004 to January 2007). The objectives of the study were (1) to investigate the temporal variation of chromium species and other matrix constituents and (2) to study the redox processes associated with the temporal variation of chromium species. Samples were collected from 15 dug wells and analyzed for chromium species and other constituents. The results showed that the groundwater was relatively more oxidizing during post-monsoon periods than the pre-monsoon periods. Except one sample, the concentration of chromium species were found in the order of Cr(VI)>Cr(III)>Cr(III)-organic complexes during all the pre- and post-monsoon periods. In most of the wells, the concentrations of Cr(III), Cr(VI), and Cr(III)-organic decreased during post-monsoon periods compared to their pre-monsoon concentrations. However, the Cr(VI)/Cr(Total) ratio still increased and the Cr(III)/Cr(Total) ratio decreased during post-monsoon periods in most of the samples. The possible mechanisms for the temporal variation of chromium species were (1) Fe(II) reduction of Cr(VI) vs oxidation of Fe(II) by dissolved oxygen and (2) oxidation of Cr(III) by Mn(IV).

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Extent of oxidation of Cr(III) to Cr(VI) under various conditions pertaining to natural environment

Cited by 189 publications

References 20 publications

Binary Component Sorption of Cadmium, and Copper Ions onto Yangtze River Sediments with Different Particle Sizes

Binary Component Sorption of Cadmium, and Copper Ions onto Yangtze River Sediments with Different Particle Sizes

Chromate Formed in a Trivalent Chromium Conversion Coating on Aluminum

Chromium speciation in a contaminated groundwater: redox processes and temporal variability

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